The present invention relates to an aerodynamic damper for an impact printing actuator.
The printing actuators used in high speed printers for data processing systems and particularly in dot matrix printers, consist of electromagnets where the actuation of a movable armature causes the printing operation.
Two kinds of actuators and two operative modes can be distinguished; that is, actuators provided with a simple electromagnetic and actuators provided with a permanent magnet, as well as actuators operating by armature attraction and actuators operating by armature release.
In actuators of the simple electromagnet type, operating in attraction mode, the movable armature, in rest position, is spaced apart from a magnetic pole and rests on a stop element.
An air gap is present between the armature and the magnetic pole.
The electromagnet energization causes the armature to be attracted against the magnetic pole and the deenergization causes the release and the return of the armature, imposed by resilient means, to the rest position.
In actuators of the simple electromagnet type, operating in release mode, the movable armature is, in rest condition, attracted against a magnetic pole, owing to the electromagnet energization.
The deenergization of the electromagnet causes the release of the armature, owing to resilient means and the consequent print operation, while the energization cuases the armature attraction in the rest position.
In the permanent magnet type actuators, which generally operate in release mode only, the movable armature, when at rest, is attracted against a magnetic pole.
The electromagnet energization causes the neutralization of the magnetic field produced by the permanent magnet and the consequent release of the armature. The deenergization of the electromagnet causes the armature to be pulled against the magnetic pole.
In all mentioned cases, it is required, to obtain high speed performance, that the armature returns to the rest position as fast as possible and without rebound.
To this purpose, dampers of various types have been used, such as resilient, ballistic, and pneumatic dampers.
Among dampers which more properly relate to the present invention, the device disclosed in U.S. Pat. No. 4,202,638 is to be mentioned.
In such patent, a stop element is provided which defines a flat surface against which a corresponding flat surface of the armature lays down.
During the armature return phase at rest position, a compressed air cushion is formed between the two surfaces. This cushion performs a braking action on the moving armature, and dampens its impact against the rest surface, reducing the rebound.
For the efficiency of the device, a relatively broad flat contacting surface is required, which is difficult to reconcile with the miniaturized structures of printing actuators currently used.
This limitation is overcome by the aerodynamic damper of the present invention which achieves a much greater efficiency by exploiting the aerodynamic pressure developed by the air flow between surfaces slighly converging and consists of a recess provided in the armature or in the rest element (or both) and having slanted walls as to the contact plane.